Low power consumption bistable microswitch

ABSTRACT

A bistable MEMS microswitch produced on a substrate and capable of electrically connecting ends of at least two conductive tracks, including a beam suspended above the surface of the substrate. The beam is embedded at its two ends and is subjected to compressive stress when it is in the non-deformed position. The beam has an electrical contact configured to produce a lateral connection with the ends of the two conductive tracks when the beam is deformed in a horizontal direction with respect to the surface of the substrate. Actuators enable the beam to be placed in a first deformed position, corresponding to a first stable state, or in a second deformed position, corresponding to a second stable state, and the electrical contact ensures connection of the ends of the two conductive tracks.

TECHNICAL FIELD

This invention relates to a low consumption bistable microswitch withhorizontal movement.

Such a microswitch is useful in particular in the field of mobiletelephony and in the space field.

RF components intended for these fields are subject to the followingspecifications:

supply voltage below 5 volts,

insulation greater than 30 dB,

insertion losses below 0.3 dB,

reliability corresponding to a number of cycles greater than 10⁹,

surface smaller than 0.05 mm²,

lowest possible consumption.

In the case of the space field in particular, some switches are usedonly one time, to switch from one state to another state in the event ofan equipment breakdown, for example. For this type of application, thereis currently a very strong interest in bistable switches, which do notrequire a supply voltage once they have switched from one state to theother.

There is also a strong interest in dual switches, which considerablysimplify the switch matrices of redundant circuits used in the case ofcritical functions. This type of application is seen in particular inthe space field (satellite antennas). These dual switches make itpossible to switch an input signal from one electronic circuit toanother in the event of a breakdown. Therefore, these switches have thepossibility of switching either a first set of two electrical tracksfrom one to the other, or a second set of two electrical tracks.

The dual switches have the advantage of enabling circuits comprisingfewer components (for example, 10 redundancy functions require 10 dualswitches rather than 20 single switches) to be produced, which means,among other things, fewer reliability tests, less assembly, increasedspace, and, overall, a lower cost.

BACKGROUND OF THE INVENTION

In the field of communications, conventional microswitches (i.e. thoseused in microelectronics) are very widely used. They are useful insignal routing, impedance-matching networks, amplifier gain adjustment,and so on. The frequency bands of the signals to be switched can rangefrom several MHz to several dozen GHz.

Conventionally, microelectronic switches have been used for these RFcircuits, which switches enable circuit electronics integration and havea lower production cost. In terms of performance, however, thesecomponents are rather limited. Thus, silicon FET switches can switchhigh-power signals at low frequencies, but not at high frequencies.MESFET (Metal Semiconductor Field Effect Transistor) switches made ofGaAs or PIN diodes work well at high frequencies, but only for low-levelsignals. Finally, in general, above 1 GHz, all of these microelectronicswitches have a significant insertion loss (conventionally around 1 to 2dB) when on and rather low insulation in the open state (from −20 to −25dB). The replacement of these conventional components with MEMS(Micro-Electro-Mechanical-System) microswitches is therefore promisingfor this type of application.

Owing to their design and operation principle, MEMS switches have thefollowing characteristics:

low insertion losses (typically lower than 0.3 dB),

high insulation in the MHz to millimetric range (typically over −30 dB),

no response nonlinearity (IP3).

Two types of contact for MEMS microswitches are distinguished: ohmiccontact and capacitive contact. In the ohmic contact switch, the two RFtracks are contacted by a short circuit (metal-metal contact). This typeof contact is suitable both for continuous signals and forhigh-frequency signals (greater than 10 GHz). In the capacitive contactswitch, an air space is electromechanically adjusted so as to obtain acapacitance variation between the closed state and the open state. Thistype of contact is particularly suitable for high frequencies (greaterthan 10 GHz) but inadequate for low frequencies.

Several major actuation principles for MEMS switches are distinguished.

Thermal actuation microswitches, which can be described as standard, arenon-bistable. They have the advantage of a low actuation voltage. Theyhave several disadvantages: excessive consumption (in particular in thecase of mobile telephone applications), low switching speed (due tothermal inertia) and the need for a supply voltage to maintain contactin the closed position.

Electrostatic actuation microswitches, which can be described asstandard, are non-bistable. They have the advantages of a high switchingspeed and a generally simple technology. They have problems ofreliability, in particular in the case of low actuation voltageelectrostatic switches (structural bonding). They also require a supplyvoltage in order to maintain contact in the closed position.

Electromagnetic actuation microswitches, which can be described asstandard, are non-bistable. They generally operate on the principle ofthe electromagnet and essentially use iron-based magnetic circuits and afield coil. They have several disadvantages. Their technology is complex(coil, magnetic material, permanent magnet in some cases, etc.). Theirconsumption is high. They also require a supply voltage in order tomaintain contact in the closed position.

Two configurations for moving the contact are differentiated: a verticalmovement and a horizontal movement.

In the case of a vertical movement, the movement occurs outside theplane of the RF tracks. The contact occurs over the top or over thebottom of the tracks. The advantage of this configuration is that themetallization of the contact pad is easy to perform (flat deposit) and,therefore, the contact resistance is low. However, this configuration ispoorly adapted for performing the function of dual contact switch. Thecontact over the top is indeed difficult to obtain. It is generallyachieved by using a contact on the cap. This configuration also has poorintegration compatibility. Indeed, for resistive switches, tracks andcontacts with gold metallization are conventionally used (good electricproperties, no oxidation). However, this metal is not integrationcompatible, even though it has been used since nearly the beginning ofthe technology for this type of configuration. There is no possibleoptimisation of the contact. Its surface can only be planar. Thestiffness of the beam forming the contact is poorly controlled. Thisstiffness is conditioned by the final form of the beam which isdependent on the topology of a sacrificial layer which is itselfdependent on the form and thickness of the tracks located below. Thebeam profile is generally irregular, which substantially increases thestiffness of the switch and therefore its actuation conditions.

In the case of horizontal movement, the movement takes place in theplane of the tracks. The contact takes place on the side of the tracks.This configuration is suitable for dual contact, with a symmetricalactuator. The “gold” metallization can be performed in the very lasttechnological step. All of the preceding steps can be compatible withthe production of integrated circuits. The form of the contact isdetermined in the photolithography step. For example, it is possible tohave a round contact so that the contact occurs at one point and so asto thus limit the contact resistance. The form of the beam is determinedin the photolithography step. Its stiffness is therefore wellcontrolled. However, the metallization on the side is delicate. Thecontact resistance can therefore be poorly controlled. Thisconfiguration is unsuitable for electrostatic actuation due to thesignificantly-reduced opposing actuation surfaces.

The number of equilibrium states is another characteristic of themovement of the switches. In the standard case, the actuator has onlyone equilibrium state. This means that one of the two states of theswitch (switched or unswitched) requires a continuous voltage supply inorder to hold it in position. The interruption of the excitation causesthe switch to move back to its equilibrium position.

In the bistable case, the actuator has two distinct equilibrium states.The advantage of this mode of operation is that the two “closed” and“open” positions of the switch are stable and do not require a powersupply when there is no switching from one state to the other.

SUMMARY OF THE INVENTION

The invention proposes a low consumption bistable microswitch withhorizontal movement. This microswitch is particularly suitable for thefield of mobile telephony and the space field.

The subject matter of the invention is therefore a bistable MEMSmicroswitch produced on a substrate and capable of electricallyconnecting the ends of at least two conductive tracks, including a beamsuspended above the surface of the substrate, wherein the beam isembedded at its two ends and subject to compressive stress when it is inthe non-deformed position, and has electrical contact-forming meansarranged to provide a lateral connection with the ends of the twoconductive tracks when the beam is deformed in a horizontal directionwith respect to the surface of the substrate, which microswitch hasmeans for actuating the beam in order to move it either into a firstdeformed position, corresponding to a first stable state, or into asecond deformed position, corresponding to a second stable state andopposite the first deformed position with respect to the non-deformedposition, wherein the electrical contact-forming means ensure theconnection of the ends of the two conductive tracks when the beam is inits first deformed position.

The microswitch can be a dual microswitch. In this case, the firstdeformed position corresponds to the connection of the ends of two firstconductive tracks, and the second deformed position corresponds to theconnection of the ends of two second conductive tracks.

It can be a single microswitch. In this case, the first deformedposition corresponds to the connection of the ends of two conductivetracks, and the second deformed position corresponds to the absence of aconnection.

According to a first embodiment, the beam is made of a dielectric orsemiconductor material and the electrical contact-forming means are madeof an electrically conductive pad integral with the beam. The actuationmeans of the beam can include thermal actuators using a bimetal effect.Each thermal actuator can then include a block of a thermally conductivematerial in close contact with an electrical resistance. The means foractuating the beam can include means for implementing electrostaticforces. They can include thermal actuators using a bimetal effect andmeans for implementing electrostatic forces.

According to a second embodiment, the beam is made of an electricallyconductive material. The means for actuating the beam can then includemeans for implementing electrostatic forces.

The electrical contact-forming means can have a form enabling them tobecome embedded between the ends of the conductive tracks to beconnected. In this case, the ends of the conductive tracks can have aflexibility enabling them to match the form of the electricalcontact-forming means in a connection.

The microswitch can also include means forming a release spring for atleast one of the embedded ends of the beam.

The electrical contact-forming means can be means providing an ohmiccontact or means providing a capacitive contact.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood, and other advantages and specialfeatures will appear from the reading of the following description,given by way of non-limiting example, accompanied by the appendeddrawings, in which:

FIG. 1 is a top view of a first alternative of the dual microswitchaccording to the present invention,

FIG. 2 shows the microswitch of FIG. 1 in a first stable operativestate,

FIG. 3 shows the microswitch of FIG. 1 in a second stable operativestate,

FIG. 4 is a top view of a second alternative of the dual microswitchaccording to the present invention,

FIG. 5 is a top view of a third alternative of the dual microswitchaccording to the present invention,

FIG. 6 is a top view of a single microswitch according to the presentinvention,

FIG. 7 is a top view of a fourth alternative of the dual microswitchaccording to the present invention,

FIG. 8 is a top view of a fifth alternative of a dual microswitchaccording to the present invention,

FIG. 9 is a top view of a sixth alternative of the dual microswitchaccording to the present invention,

FIG. 10 is a top view of a dual microswitch corresponding to the firstalternative but provided with optimised contacts,

FIG. 11 shows the microswitch of FIG. 10 in a first stable operativestate.

DETAILED DESCRIPTION

The remainder of the description will relate, by way of example, toohmic contact microswitches. However, a person skilled in the art caneasily apply the invention to capacitive contact microswitches.

FIG. 1 is a top view of a first alternative of the dual microswitchaccording to the first invention.

The microswitch is produced on a substrate 1 of which only a portion isshown for the sake of simplification. This microswitch is a dual switch.It is intended to produce a connection either between the ends 12 and 13of conductive tracks 2 and 3, or between the ends 14 and 15 ofconductive tracks 4 and 5.

The microswitch of FIG. 1 includes a beam 6 made of a dielectric orsemiconductor material. It is located in the plane of the conductivetracks. The beam is embedded at its two ends in elevated portions of thesubstrate 1. It is shown in its initial position and is then subjectedto a compressive stress. This stress can be caused by the intrinsicstresses of the materials used to form the mobile structure of themicroswitch, i.e. the beam and the associated elements (actuators).

The beam shown has a rectangular cross-section. On its surface directedtoward tracks 2 and 3 (i.e. on one of its sides), it supports actuators20 and 30 and, on its surface directed toward tracks 4 and 5 (i.e. onits other side), it supports actuators 40 and 50. The actuators arelocated near the embedded areas of the beam. Each actuator consists of athermally conductive block with an electrical resistance. Thus, theactuator 20 includes a block 21 to which a resistance 22 is connected.The same is true of the other actuators.

The beam is preferably made of a dielectric or semiconductor materialwith a low thermal expansion coefficient. The blocks of the thermalactuators are preferably made of a metal material with a high thermalexpansion coefficient so as to obtain an efficient bimetal effect. Asthe movement of the beam occurs in the horizontal direction (the planeof the figure), the actuators are placed on the sides of the beam andnear the embeddings, always for the purpose of thermomechanicalefficiency.

The beam 6 also supports, in the central portion and on its sides, anelectrical contact pad 7, intended to provide an ohmic electricalconnection between the ends 12 and 13 of the tracks 2 and 3, and anelectrical contact pad 8 between the ends 14 and 15 of the tracks 4 and5.

When the microswitch is activated, a first set of actuators enables thebeam 6 to switch into a position corresponding to one of its two stablestates. This is shown in FIG. 2. The actuators 40 and 50 create abimetal effect in the beam 6, which is deformed so as to move into afirst stable state shown in the figure. In this stable state, theelectrical contact pad 7 provides a connection between the ends 12 and13 of conductive tracks 2 and 3. The power supplies of the electricalresistances of the actuators 40 and 50 are interrupted and the beamremains in this first stable state.

To switch the microswitch, i.e. to move it into its second stable state,the electrical resistances of the actuators 20 and 30 must be powered inorder to induce a bimetal effect unlike the previous in the beam 6. Thelatter is deformed so as to move into its second stable state shown inFIG. 3. In this second stable state, the electrical contact pad 8provides a connection between the ends 14 and 15 of conductive tracks 4and 5. The power supplies of the electrical resistances of the actuators20 and 30 are interrupted and the beam remains in this second stablestate.

The electrical resistances of the actuators are preferably made of aconductive material with high resistivity. The conductive tracks and thecontact pads are preferably made of gold for its good electricalproperties and its reliability over time, in particular with regard tooxidation.

The embeddings of the beam may be either rigid (simple embedding), ormore or less flexible by adjusting the configuration of the embeddings,for example, by adding release springs. The ability to adjust theflexibility of the beam enables the stresses in the beam to becontrolled both initially (intrinsic stresses) and in order to go fromone stable state to the other (passing through a buckling state). Thishas the advantage of limiting the risks of breakage of the beam, butalso of enabling the consumption of the microswitch to be limited(lowering the switching temperature of the microswitch). The stresses ofthe beam can be relaxed only at one of its embedded ends or at both ofits ends.

FIG. 4 is a top view of a second alternative of a dual microswitchaccording to the present invention, and therefore the two ends of thebeam have an embedding with stress relaxation.

The alternative embodiment of FIG. 4 includes the same elements as thealternative embodiment of FIG. 2, with the exception of the embedding ofthe ends of the beam. At this level, the substrate 1 has stressrelaxation slots 111 perpendicular to the axis of the beam. The slots111 provide a certain flexibility to the substrate portion locatedbetween said slots and the beam. The microswitch is shown in its initialposition, before its activation.

The use of electrostatic forces can also be considered for themicroswitch according to the invention, either as an actuationprinciple, or as an assistance in the switched position afterinterruption of the power supply of the electric heating resistors ofthe actuators, in order to increase the pressure of the electricalcontact pad and thus limit the contact resistance.

FIG. 5 is a top view of a third alternative of a dual microswitchaccording to the present invention. This microswitch uses bimetal effectactuators and has electrostatic assistance. It is shown in its initialposition, before its activation.

The substrate 201, tracks 202 and 203 to be connected by the contact pad207 when the beam 206 is switched into a first stable state, tracks 204and 205 to be connected by the contact pad 208 when the beam 206 isswitched into a second stable state, and actuators 220, 230 and 240,250, are recognised.

The microswitch of FIG. 5 also comprises electrodes enablingelectrostatic forces to be applied. These electrodes are distributed onthe beam and on the substrate. The beam 206 supports electrodes 261 and262 on a first side, and electrodes 263 and 264 on a second side. Theseelectrodes are located between the thermal actuators and the electricalcontact pads. The substrate 201 supports electrodes 271 to 274 oppositeeach electrode supported by the beam 206. Electrode 271 has a portionopposite electrode 261, which portion is not visible in the figure, anda portion intended for its electrical connection, which part is visiblein the figure. The same applies to electrodes 272, 273 and 274 withrespect to electrodes 262, 263 and 264, respectively.

It is noted that electrodes 271 to 274 have a form that corresponds tothe form of the deformed beam. This enables the actuation or maintainingvoltages to be limited (variable gap electrodes).

The microswitch can be put in a first stable state, for example,corresponding to the connection of the conductive tracks 202 and 203 bythe contact pad 207, by means of thermal actuators 240 and 250 which areactivated only to obtain the first stable state. The application of avoltage between electrodes 261 and 271 and between electrodes 262 and272 ensures a reduction in the contact resistance between the pads 207and the tracks 202 and 203.

The microswitch can be put in the second stable state by means ofactuators 220 and 230 which are activated only to obtain the switchingfrom the first stable state to the second stable state. The applicationof a voltage between electrodes 263 and 273 and between electrodes 264and 274 ensures a reduction in the contact resistance between the pad208 and the tracks 204 and 205.

FIG. 6 is a top view of a single microswitch according to the presentinvention. This microswitch uses bimetal-effect actuators, withoutelectrostatic assistance. It is shown in its initial position, beforeits activation.

The substrate 301 and tracks 302 and 303 to be connected by the contactpad 307 when the beam 306 is switched into a first stable state arerecognised, and the second stable state corresponds to an absence of aconnection. Actuators 320, 330 and 340, 350 are also recognised.

FIG. 7 is a top view of a fourth alternative of the dual microswitchaccording to the present invention. This microswitch uses onlyelectrostatic-effect actuators. It is shown in its initial position,before its activation.

The substrate 401, tracks 402 and 403 to be connected by the contact pad407 when the beam 406 is switched into a first stable state and tracks404 and 405 to be connected by the contact pad 408 when the beam 406 isswitched into a second stable state, are recognised.

The microswitch of FIG. 7 comprises electrodes enabling electrostaticforces to be applied. These electrodes are distributed over the beam andthe substrate. The beam 406 supports electrodes 461 and 462 on a firstside and electrodes 463 and 464 on a second side. These electrodes arelocated on each side of the electrical contact pads 407 and 408. Thesubstrate 401 supports electrodes 471 and 474 opposite each electrodesupported by the beam 406. The electrode 471 has a portion opposite theelectrode 461, which portion is not visible in the figure, and a portionintended for its electrical connection, which is visible in the figure.The same applies to electrodes 472, 473 and 474 with respect toelectrodes 462, 463 and 464, respectively.

The microswitch can be put in a first stable state, for example,corresponding to the connection of the conductive tracks 402 and 403 bythe contact pad 407, by applying a voltage between electrodes 461 and471 and between electrodes 462 and 472. Once the beam has switched intoits first stable state, the applied voltage can be removed or reduced soas to reduce the contact resistance between the pad 407 and the tracks402 and 403.

The microswitch can be put in the second stable state by applying avoltage between electrodes 463 and 473 and between electrodes 464 and474 (and removing the electrostatic assistance voltage for keeping it inthe first stable state if this assistance has been used). Once the beamhas switched into its second stable state, the applied voltage can beremoved or reduced, as above.

FIG. 8 is a top view of a fifth alternative of a dual microswitchaccording to the present invention. This fifth alternative is anoptimised version of the previous alternative. The same references as inthe previous line have been used to designate the same elements.

Electrodes 471′, 472′, 473′ and 474′ have the same function as thecorresponding electrodes 471, 472, 473 and 474 of the microswitch ofFIG. 7. However, they have a form that corresponds to the form of thedeformed beam. This enables the actuation or maintenance voltages to belimited (variable gap electrodes).

FIG. 9 is a top view of a sixth alternative of a dual microswitchaccording to the present invention. It is shown in its initial positionbefore its activation.

The substrate 501, tracks 502 and 503 to be connected by the contact pad507 when the beam 506 is switched into a first stable state and tracks504 and 505 to be connected by the contact pad 508 when the beam 506 isswitched into a second stable state are recognised.

The beam 506 in this alternative is a metal beam, for example, made ofaluminium, supporting contact pads 507 and 508 on its sides. Theswitching of the beam into a first stable state, for example,corresponding to the connection of the conductive tracks 502 and 503 isachieved by applying a switching voltage between the beam 506 acting asan electrode and electrodes 571 and 572. Once the beam has switched intoits first stable state, the applied voltage can be removed or reduced soas to reduce the contact resistance between the pad 507 and the tracks502 and 503.

The microswitch can be put in the second stable state by applying avoltage between the beam 506 and electrodes 573 and 574 (and removingthe electrostatic assistance voltage for keeping it in the first stablestate if this assistance has been used). Once the beam has switched intoits second stable state, the applied voltage can be removed or reduced,as above. For this microswitch alternative, the electrostatic actuationhas been optimised by the form given to electrodes 571 to 574.

FIG. 10 is a top view of a dual microswitch corresponding to the firstalternative but provided with optimised contacts. The microswitch isshown in its initial position before its activation. The same referencesas in FIG. 1 have been used to designate the same elements.

It is noted in this figure that the ends 12′, 13′, 14′ and 15′ ofconductive tracks 2, 3, 4 and 5, respectively, have been optimised inorder to provide better electrical contact with the contact pads 7′ and8′. Thus, the contact pads 7′ and 8′ have a broader form at their base(i.e. near the beam) than at their top. They can thus be more easilyembedded between the ends 12′, 13′, and 14′, 15′, which are providedwith an embedding groove.

The ends of the conductive tracks can also be slightly flexible so a tomatch the form of the contact pad and thus provide better electricalcontact. This is shown in FIG. 11, where the microswitch is shown in afirst stable state.

The microswitch according to the present invention has the followingadvantages.

Its operation requires low consumption due to the bistability.

The alternatives with a thermal actuator have a high actuationefficiency. Their switching time is low insofar as it is not necessaryfor the temperature to rise very high in order to cause the beam toswitch. They also have a low switching voltage when electrostaticactuators are connected to the thermal actuators. This is due to:

the use of the thermal bimetal effect;

the use of electric heating resistors integrated into the beam andlocated on (or in the close vicinity of) portions with a high thermalexpansion coefficient of the bimetal (metal blocks) enabling theelectrothermal efficiency to be as high as possible (lowest thermallosses);

the use of a dielectric beam with low thermal conductivity, preventingsignificant heat dissipation outside the bimetal zone.

Therefore, the invention uses both the difference in thermal expansionof two different materials, and the application and conditioning of thetemperature of the heating resistors at the level of the bimetal.

The invention provides the possibility of obtaining a dual switch.

It provides the possibility of obtaining a switch in which the contactresistance can be optimised:

by the form which can be given to the contact pads and to the ends ofthe tracks to be switched, and optionally the flexibility of the,contact zone which allows for a more “suitable” contact between contactpads and tracks;

by the possibility of adding “assistance” electrodes with a suitableform, which make it possible to obtain a high pressure on the contactpad with a low voltage at the terminals of these electrodes.

The production of microswitches according to the invention is highlycompatible with the methods for producing integrated circuits (“gold”metallizations at the end of the production process, if necessary).

The bistability of the microswitch is perfectly controlled for tworeasons. The first reason is that the bistability is obtained by thefact that the beam must be subjected to compression stress. This stressis created by the materials constituting the switch (form, thickness).If the beam is designed so as to be perfectly symmetrical, and if eachof the two sets of actuators is produced in the same deposit, the stresscan only be perfectly symmetrical (same form, same thickness andsymmetry of the actuators). The result is a device likely not to favourone stable state over another state that would be less stable. Thesecond reason is that it is possible to control the value of thecompression stress by the type of deposit and also by the design, byadding stress release “springs”.

The microswitch according to the invention can advantageously beproduced on a silicon substrate. The embedded portion and the beam canbe made of Si₃N₄, SiO₂ or polycrystalline silicon. The conductivetracks, contact pads, electrodes and thermal actuators can be made ofgold, aluminium or copper, nickel, materials capable of being vacuumdeposited or electrochemically deposited (electrolysis, autocatalyticplating). The heating resistors can be made of TaN, TiN or Ti.

For example, a method for producing an ohmic microswitch with thermalactuation on a silicon substrate can include the following steps:

deposition of an oxide layer of 1 μm of thickness by PECVD onto thesubstrate,

lithography and etching of a cavity for the embedding,

deposition of a polyimide layer of 1 μm of thickness, acting as asacrificial layer,

dry planarisation or chemical mechanical polishing (CMP) of thesacrificial layer,

deposition of a SiO₂ layer of 3 μm of thickness,

etching of said SiO₂ layer so as to obtain openings for the actuators,the contact pads and the conductive tracks,

deposition of an aluminium layer of 3 μm of thickness,

planarisation by CMP of the aluminium layer until the SiO₂ layer isuncovered,

deposition of a SiO₂ layer of 0.15 μm of thickness,

deposition of a TiN layer of 0.2 μm of thickness,

lithographic etching of the heating resistors in the TiN layer,

deposition of a SiO₂ layer of 0.2 μm of thickness,

lithographic etching of this SiO₂ layer so as to obtain contact pads ofthe heating resistors,

lithographic etching of the SiO₂, stopping at the sacrificial layer soas to obtain the beam,

deposition of a Cr/Au bilayer of 0.3 μm of thickness,

lithographic etching of the conductive tracks and contact pads,

etching of the sacrificial layer so as to expose the beam.

According to another embodiment, a method for producing microswitch withthermal actuation on a silicon substrate can include the followingsteps:

deposition of an oxide layer of 1 μm of thickness by PECVD onto thesubstrate,

lithographic etching of a cavity for the embedding,

deposition of a polyimide layer of 1 μm of thickness, acting as asacrificial layer,

dry planarisation or chemical mechanical polishing (CMP) of thesacrificial layer,

deposition of a Sio₂ layer of 3 μm of thickness,

etching of said SiO₂ layer so as to obtain openings for the actuators,

deposition of an aluminium layer of 3 μm of thickness,

planarisation by CMP of the actuators,

deposition of a TiN layer of 0.2 μm of thickness,

lithographic etching of the heating resistors in the TiN layer,

deposition of a SiO₂ layer of 0.2 μm of thickness,

lithographic etching of this SiO₂ layer so as to obtain contact pads ofthe heating resistors,

lithographic etching of said SiO₂ layer on a depth of 3.2 μm so as toobtain the beam,

deposition of a Ti/Ni/Au trilayer of 1 μm of thickness,

lithographic etching of the conductive tracks and contact pads,

etching of the sacrificial layer so as to expose the beam.

1-15. (canceled)
 16. A bistable MEMS microswitch produced on a substrateand configured to electrically connect ends of at least two conductivetracks, including a beam suspended above a surface of the substrate,wherein the beam is embedded at its two ends and is subjected tocompressive stress when the beam is in a non-deformed position, whereinthe beam includes an electrical contact-forming mechanism configured toproduce a lateral connection with ends of the two conductive tracks whenthe beam is deformed in a horizontal direction with respect to thesurface of the substrate, the microswitch comprising: means foractuating the beam so as to place the beam either in a first deformedposition, corresponding to a first stable state, or in a second deformedposition, corresponding to a second stable state and opposite the firstdeformed position with respect to the non-deformed position, wherein theelectrical contact-forming mechanism ensures connection of the ends ofthe two conductive tracks when the beam is in its deformed position. 17.A microswitch according to claim 16, wherein the microswitch is a dualmicroswitch, and the first deformed position corresponds to connectionof ends of two first conductive tracks, and the second deformed positioncorresponds to connection of ends of two second conductive tracks.
 18. Amicroswitch according to claim 16, wherein the microswitch is a singlemicroswitch, and the first deformed position corresponds to connectionof the ends of two conductive tracks and the second deformed positioncorresponds to an absence of a connection.
 19. A microswitch accordingto claim 16, wherein the beam is made of a dielectric or semiconductormaterial and the electrical contact-forming mechanism includes anelectrically conductive pad integrated into the beam.
 20. A microswitchaccording to claim 19, wherein the means for actuating the beam includesthermal actuators using a bimetal effect.
 21. A microswitch according toclaim 20, wherein each thermal actuator includes a block of thermallyconductive material in contact with an electrical resistance.
 22. Amicroswitch according to claim 19, wherein the means for actuating thebeam includes means for implementing electrostatic forces.
 23. Amicroswitch according to claim 19, wherein the means for actuating thebeam includes thermal actuators using a bimetal effect and means forimplementing electrostatic forces.
 24. A microswitch according to claim16, wherein the beam is made of an electrically-conductive material. 25.A microswitch according to claim 24, wherein the means for actuating thebeam includes means for implementing electrostatic forces.
 26. Amicroswitch according to claim 16, wherein the electricalcontact-forming means mechanism is configured to be embedded between theends of the conductive tracks to be connected.
 27. A microswitchaccording to claim 26, wherein the ends of the conductive tracks have aflexibility enabling them to match the form of the electricalcontact-forming mechanism during a connection.
 28. A microswitchaccording to claim 16, further comprising release spring-forming meansfor at least one of the embedded ends of the beam.
 29. A microswitchaccording to claim 16, wherein the electrical contact-forming mechanismprovides an ohmic contact.
 30. A microswitch according to claim 16,wherein the electrical contact-forming mechanism provides a capacitivecontact.